What are the advantages of planting legumes with other crops?

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Legumes are plants such as beans, peanuts, peas and lentils. In addition to being good sources of nutrition they have the ability to "fix" nitrogen. This means the plants, and the bacteria that live symbiotically in their roots, can change nitrogen from a form animals and plants cannot use into one that they can. Nitrogen is vital for life;it forms parts of our DNA and proteins. Our atmosphere is largely nitrogen, but it is in a form, N2 (nitrogen gas), that living things can't utilize. Nitrogen "fixing" means it is chemically changed into NH3 (ammonia), which living things can use. When legumes are planted with other crops that do not have this ability, it can help thse crops by supplying nitrogen in a usable form. In practice, this ability of legumes to fix nitrogen is more likely to be used as a system of crop rotation, rather than planting crops close enough to each other for this advantage. Fertilizers to supply nitrogen (and other nutrients) are generally used on commercial crops, but using crop rotation, so that legumes alternate with other crops, usually reduces the amount of fertilizer needed.

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